Minneapolis Net Zero House

When the Hanson's built their first home in a suburb of Minneapolis, Minnesota, back in 2006, they were not trying to get to Net-Zero. The concept had hardly been on anyone's radar over a decade ago. But they wanted it to be as energy-efficient as possible. So, they installed spray foam insulation, geothermal, and solar panels. "It was basically like taping energy efficiency post-it notes onto a house," says Mark. 

The problem was that their builders did not look at the home and site holistically, missing opportunities that would have made the home more functional. As they discovered after living in it, it was a much bigger house than two people needed. They also had a long commute to and from work each day.

It's All About Setting Goals

The primary goal for the Hansons was to have a truly Net Zero energy home, but it didn't stop there. They wanted the house to be Net Zero, including the ability to charge their two electric vehicles, their electric lawnmower and snowblower. 

A second goal was to have a smaller, beautiful and comfortable home, one that they could live in for the rest of their lives—so everything the need is on the main level. 

Third, they wanted to make sure the home was healthy and that it did not contribute in any way to something that could harm other people's health. They focused on using healthy materials, e.g., paints, cabinets, and adhesives that do not off-gas. They also thought about the site. They wanted to manage stormwater on their property and even pull some of the water off the adjacent roads. This would prevent it from running through the streets, where stormwater can pick up pollutants that end up in our drinking water. 

So, what was the driving force behind these lofty goals? As Mark says, he has always lived by the axiom, "We do not inherit the earth from our ancestors; we borrow it from our children." He continues, "I just believe we should leave this world a better place than we found it."

Having been concerned about the environment and climate change for a few decades, they set out to do what they could with their home. They asked themselves, "What can we do? We can build a house that meets our values and morals." And that they did.

Designing the Home

Having the goal of Net Zero energy meant the house needed to have a tight envelope, be well insulated, and south-facing to take advantage of the sun's heat during the winter. It also needed to be designed for solar panels, so there are two large south-facing roofs that hold an 18.9-kilowatt (kW) system of panels. Able to plan ahead (and unlike their first house), they made sure there were no vents on the south-facing roofs.

The entire house was designed to run solely on electricity, with no natural gas line on the property. Having nothing to combust means that there are fewer vents, so the building envelope is naturally tighter, which means it's easier to keep warm or cool. It also means their carbon monoxide detectors will never go off, though they had to install them to comply with building code.

For back-up power, they avoided a gas generator. They stuck with electricity by installing a Tesla Powerwall battery pack in their garage. Mark manages an app that allows him to choose how much of the power their home produces goes back to the grid or gets stored in their batteries. In the winter, for example, they want more storage in the batteries in the event of a power outage. The solar panels won't produce enough during the short days to cover their needs at night, and the house must have some power in the winter. In the summer, though, they use energy from the battery at night, and only reserve about 10% for back-up. Why? Because having back-up power in the summer is not as critical, and the panels will produce more during the longer days to meet their needs. "We like to think we are sharing this power with the neighbors," Kate says.